1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a wireless communication system supporting multiple carriers.
2. Related Art
A wireless communication system generally uses a single bandwidth in order to transmit data. For example, the second-generation wireless communication system uses a bandwidth 200 KHz to 1.25 MHz and the third-generation wireless communication system uses a bandwidth of 5 MHz to 10 MHz. In order to support increasing transmission capacity, in the LTE (long term evolution) or the IEEE 802.16m of the recent 3rd generation partnership project (3GPP), a bandwidth has been continuously extended up to 20 MHz or more. It is necessary to increase a bandwidth in order to increase transmission capacity. However, it is not easy to allocate a frequency having a large bandwidth except some areas around the world.
As a technology for efficiently using a segmented small band, a carrier aggregation (CA) technology for generating an effect such as using a logical large band by bundling a plurality of physically non-continuous bands in a frequency domain has been developed. An individual unit carrier bundled by the carrier aggregation is referred to as component carrier (CC). Each component carrier is defined by a single bandwidth and a center frequency.
A system capable of transmitting and/or receiving data in a wide band through a plurality of component carriers is referred to as a multiple component carrier system or a carrier aggregation environment. The multiple component carrier system simultaneously supports a narrow band and a wide band by using one or more carrier. For example, when the single carrier corresponds to a bandwidth of 5 MHz, the multiple component carrier system may support a bandwidth of maximum 20 MHz by using four carriers.
In order to operate the multiple component carrier system, various control signaling is required between a base station and a user equipment. For example, exchange of acknowledgement (ACK)/not-acknowledgement (NACK) information for performing hybrid automatic repeat request (HARQ), exchange of a channel quality indicator (CQI) indicating quality of a downlink channel, and the like, are required.